Production of threads of thermoplastic cellulose derivatives



Feb- 5, 1952 H. M. AVERNS ET Al. 2,584,779

PRODUCTION OF THREADSVOF THERMOPLASTIC CELLULOSE DERIVATIVES Filed OCC. 15, 1948 .//7 Ven fors Harry Maar/ce Aver/7s MMM Patented Feb. 5, 1952 UNTED STATS ortica PRDUCTION OF THREADS 0F THERMO- PLASTIC CELLULSE DERIVATIVES British company vApplication October 15, 1948, Serial No.54,624 vIn Great Britain November 12, 1947 3 Claims.

This invention relates to the production of threads of thermoplastic cellulose derivatives such as cellulose esters or ethers and in particular cellulose acetate; The term threads is used broadly in this specification to include iibres, iilarnents, threads, yarns. cords and like rilainentary materials.

In the production of cellulose acetate and like threads it is well-'known to stretch the threads which have been brought to vsuitable condition after their formation in order to improve the tenacity. It is also known that the stretching operations generally cause a loss in extensibility, that is the percentage increase in length at the breaking point of the dry thread, so that in general an increase in tenacity is only obtained at ythe expense of a loss in extensibility. This behaviour is demonstrated by the following figures obtained with one unstretched cellulose acetate thread having a dry tenacity of 1.15 grams per denier and 36 per cent extensibility; on hot stretching this thread 50 per cent the tenacity rose to 2.0 grains per denier and the extensibility fell to 16.0 per cent; on stretching 100 per cent ythe tenacity was 2.50 grams per denier and the extensibility was 10.0 per cent; on stretching 150 per cent the tenacity was 2.7 grams per denier and the extensibility was "I per cent; further stretching had little effect on the extensibility which remained fairly constant at 6 to 7 per cent. y

It has already been proposed in United States specification No. 1,921,426 to treat artificial silk laments, the basis of which is cellulose acetate or other cellulose esters or ethers or mixtures thereof, by stretching the dry filaments when they have been brought to the plastic state by heating at a suitable temperature. In the example given in United States specification No. 1,921,426 a thread having an initial dry tenacity of 1.3 grams per denier and an extensibility of 28 per cent is stretched 100 per cent whereupon the tenacity has risen to 2 grams per denier and the extensibility has fallen to 12 per cent.

During normal weaving operations, the threads being Woven are generally subjected to varying tension and moreover the tension may at some stages reach a high value. When Weaving threads of low extensibility there is consequently a :pronounced tendency for the threads `to break during the weaving.

The object of the present invention is to produce high tenacity threads of thermo-plastic cellulose derivatives which have a sufficient extensibility for normal weaving purposes'.

In accordance with the present invention, a

process for the production of high tenacity threads of Ithermoplastic cellulose derivatives suitable for Weaving comprises the steps of heating preformed threads of the thermoplastic cellulose derivative to a .temperature suflicient to render them plastic, stretching the threads at .least 50 per cent while they are in the plastic state, and subsequently .permitting the threads tc shrink at least 8 per cent While they are in a heated plastic state. The stretching and shrinking steps may be carried out While the threads are conveyed through a single heating chamber but are preferably e'iected in separate heating chambers. K

l'n a preferred form of the present invention the stretching of the plastic thread is effected in two stages, the thread being stretched in the iirst stage at least 40 per cent and in the second stage a lower degree of stretch may be used, for example 30 per cent.

The preferred range ior the single stretching operation is from 4G to 300 per 'cent and for the .two-stage stretching operation the preferred phere before collecting the thread; if desired 'a current of air at ordinary temperature may also be directed onto the thread. The treatment of the thread with air in this manner allows the thread to become dimensionally stable before it Yis collected.

In carrying out the process according to the invention, the stretching of the plastic thread increases the tenacity and reduces the extensibility and the subsequent shrinking of the thread has littlel eiect on the tenacity but 'causes 'an `appreciable increase in the extensibility.

The process of the invention is preferably conducted continuously with the help of the apparatus diagrammatically illustrated in the accompanying drawing. In this apparatus, three vertical heating tubes I, 2, 3, preferably electrically heated, are arranged alongside each other and four rotating rollers, 4, 5, 6, 1, for example godets, the diameters and speeds of which are such as to ensure stretching of the thread as it 3 passes through each of the first two heating tubes I and 2 and shrinkage as it passes through the third heating tube 3. In operation, cellulose acetate thread 8 is drawn from a bobbin 9 and is passed with the aid or xed guides I0, I I, twice around the first roller 4, then up through the air and with the aid of further guides I2, I3 down through the rst heating tube I and around the second roller 5 which as shown is on a common driving shaft with, and is of larger diameter than, the rst roller 4, then with the aid of guides I4, I5, I6, II up through the air and down through the second heating tube 2 and around the third roller 6 which is of smaller diameter than the second roller 5 but is driven at a higher speed of rotation, then once again with the aid of guides I8, I9, 2i), 2| up -through the air and down through the third heating tube 3 on to the fourth roller 'I which is on a common driving shaft with,

Ibut is of smaller' diameter than, the third roller Example 1 The apparatus described above with reference to the drawing was used for stretching dry-spun acetone-free cellulose acetate thread. thread had a dry tenacity of 1.15 grams per denier and a 36 per cent extensibility. The temperature of the three heating tubes I, 2 and 3 was approximately 280 centigrade and each tube was 40 inches long. The diameters of the rst and sece ond wheels A and 5 were designed to give a iirststage stretch of rI5 per cent, the diameters and speeds of the second and third wheels 5 and 6 were designed to give a second-stage stretch of 40 per cent, and the diameters of the third and fourth Wheels 6 and 1 were designed to give a shrinkage of 12 per cent. The withdrawal speed of the yarn 8 was 75 metres per minute.

After the first stage (75 per cent) stretch the tenacity of the thread was 2.10 grams per denier and the extensibility was 13 per cent. After the second stage stretch the tenacity was 2.40 grams per denier and the extensibility was per cent. After the shrinking step the tenacity was 2.30

grams per denier and the extensibility was 15 per cent.

Example 2 A single stretching operation was carried out in exactly the same manner as the rst stage stretching operation of Example 1, to give a 75 per cent stretch and the shrinking step was designed to give 10 per cent shrinkage.

The stretched yarn, as in Example 1 had a tenacity of 2.10 grams per denier and an extensibility of 13 per cent. After shrinkage the This tenacity was 2.0 grams per denier and the extensibility was per cent.

In carrying out the above examples, it is not essential to carry out the process continuously. The thread from the second wheel 5 may be collected on a bobbin and subsequently reheated and then stretched and shrunk, or shrunk only. as a separate operation. l

The temperature of the stretching tube may be varied, depending on the speed of the stretching, the percentage of stretch and the properties required in the nal yarn; for example *with*v cellur7 from2l0?.

lose acetate, the temperature may vary to 360 centigrade according to condi44 'Ihe degree of shrinkage may also desired to give diiierent extensibilitie l Example l, using a shrinkage of 15 to 20 p ;cent, the extensibility may be increased to 17 peigcent.

What we claim is:

1. A process for the production of high tenacity threads of cellulose acetate suitable for weaving. consisting in heating dry preformed threads of cellulose acetate to a temperature in the range of 210 to 360 centigrade to render them plastic and simultaneously stretching them at least per cent while they are in the dry heated plastic state, whereby the tenacity of the thread is increased to at least two grams per denier and its extensibility correspondingly reduced, and subsequently reheating the dry threads to a temperature within the range of 210 to 360 centigrade to render them plastic and simultaneously permitting the threads to shrink from about l0 per cent to about 20 per cent while they are in the dry heated plastic state, whereby the extensibility of the thread is increased to at least 14 per cent, the plasticity of the thread during both the stretching and the shrinking steps being effected solely by the action of the heat.

2. A process as claimed in claim 1 wherein the stretching is effected in two stages.

3. A process as claimed in claim 2 wherein the thread is stretched from about 40 per cent to about per cent in the rst stage and from about 20 per cent to about 150 per cent in the second stage.

H. M. AVERNS. J. STRAW'.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

1. A PROCESS FOR THE PRODUCTION OF HIGH TENACITY THREADS OF CELLULOSE ACETATE SUITABLE FOR WEAVING CONSISTING IN HEATING DRY PREFORMED THREADS OF CELLULOSE ACETATE TO A TEMPERATURE IN THE RANGE OF 210* TO 360* CENTIGRADE TO RENDER THEM PLASTIC AND SIMULTANEOUSLY STRETCHING THEM AT LEAST 50 PER CENT WHLE THEY ARE IN THE DRY HEATED PLASTIC STATE, WHEREBY THE TENACITY OF THE THREAD IS INCREASED TO AT LEAST TWO GRAMS PER DENIER AND ITS EXTENSIBILITY CORRESPONDING REDUCED, AND SUBSEQUENTLY REHEATING THE DRY THREADS TO A TEMPERATURE WITHIN THE RANGE OF 210* TO 360* CENTIGRADE TO RENDER THEM PLASTIC AND SIMULTANEOUSLY PERMITTING THE THREADS TO SHRINK FROM ABOUT 10 PER CENT OT ABOUT 20 PER CENT WHILE THEY ARE IN THE DRY HEATED PLASTIC STATE, WHEREBY THE EXTENSIBILITY OF THE THREAD IS INCREASED TO AT LEAST 14 PER CENT, THE PLASTICITY OF THE THREAD DURING BOTH THE STRETCHING AND THE SHRINKING STEPS BEING EFFECTED SOLELY BY THE ACTION OF THE HEAT. 